Process of oxidizing naphthalene and related condensed aromatic ring compounds



NOV. 21, o EST 51' AL PROCESS OF OXIDIZING NAPHTHALENE AND RELATEDCONDENSED AROMATIC RING COMPOUNDS Filed Jan. 31, 1930 2 Sheets-Sheet lINVENTOR-S WITNESSES a, walla/M 0 r JAVA-C4 3/5 QM Nov. 21, 1933. QFORREST r AL 1,936,427

PROCESS OF OXIDIZING NAPHTHALENE AND RELATED CONDENSED AROMATIC RINGCOMPOUNDS Filed Jan. 31, 1930 2 Sheets-Sheet 2 wrmsssss g y 4V v 02 Sumfi dow Patented Nov. 21, 1933 PROCESS OF OXIDIZENG NAPl-ITHALENE ANDRELATED CONEEN$E Z AROMATIC RING COMPOUNDS Henry 0. Forrest, Andover,Mass, and For IQ V Fr l chi. Eli a-h h, N. J... ass n s o Na ionaSynthetic Corporation, Painesville, Ohio, a cor.- V

poration of Delaware Application January 31, 1930.' Serial No.424,906

8 Claims. 01. 260-108) This invention relates to direct oxidationprocesses, and especially to the partial oxidation of cyclic organiccompounds.

The processes heretofore known and practiced for the commercialproduction of oxygenated aromatic or cyclic organic compounds are opento numerous objections. For example, in the prior liquid phase processesan active agent, such as an alkali, a catalyst, has been necessary, oran intermediate compound has been used, such as benzyl chloride in theproduction of oenzoic acid from toluene, or else the necessary oxygenhas been generated in a solution or suspension of the compound to beoxidized. Consequently it may be said that the prior liquid phaseprocesses are of an indirect nature, and are subject to the limitationsof such processes. Thus, the use of auxiliary active agents and the likemay cause losses due to side reactions, and the use of a plurality ofsteps engenders decreased yields,

and the oxygenated product may be contaminated. Furthermore, the activeagents and formation of intermediates add to the cost.

Vapor phase processes are ofa more direct nature than those justreferred to, and because they are free from many of the disadvantages ofindirect processes, many vapor phase proc esses have been proposed andused for the oxidation of aromatic compounds to produce more usefulproducts. All oxidation processes, however, are exothermic, andconsequently there is a tendency toward complete degeneration to carhondioxide, To produce useful yields of a desired oxidation product thiseffect must be minimized by careful and accurate temperature control ofboth liquid and vapor phase processes. Such temperature control isparticularly diiiicult in vapor phase processes, because of the-inherentdifficulty of regulating vapor temperatures, and because the processesunder'consideration are all catalytic.

Vapor phase processes require the treatment of large volumes of gases,and even under the best conditions of operation it has not been possibleto maintain the entire body of gas in the reaction zone at a uniformtemperature. That is, although the gases at a heat-exchanging surfacemay be at proper temperature, the temperature inwardly from the wallwill be above optimum. Or, if the center of the reaction zone ismaintained at optimum temperature, the temperature gradient is such thatthe gases at the wall are too cool. Consequently, the oxidationprocesses previously proposed for use with cyclic organic compounds havebeen inefficient, being. attended by high carbon dioxide formation, orby low conversion efiiciencies, Also, it is characteristic of priorprocesses that the ring is usually broken With, production of lessvaluable products.

In consequence of theseand' other disadvantages of thepriorprocessesthere has been no completely satisfactory process available upto the present time for the commercial oxidation of cyclic organiccompounds, all such processes bein subject to the disadvantages referredto, and being also subject to the known difiiculties and disadvantageswhich the use of catalysts and other active agents present.

It is an object of this invention to provide a process for the partialoxidation of cyclic organic compounds, which effects direct oxidation tothe desired product, produces useful yields and mini: mines sidereactions and complete degeneration to carbon dioxide, usesanoxygen-containing gas, preferably air, as the oxidizing mediurp,.lsapplicable generally to the oxidation of compounds of the type referredto, is simple eflicient and readily controlled, and satisfactorilyevercomes many of the disadvantagesv of prior processes. I

Among others itis a particular object to pro-1 vide a process of thetype referred to in which active agents are not required, which makesuse of the liquid phase, provides ready and accurate temperaturecontrol, does not requireelaborate or unduly expensive apparatus, andwhich produces a maximum of products retaining a ring structure.

The accompanying drawings show. two types of apparatus which may be usedin the practice of the invention, in which Fig. l is schematic drawingshowing apparatus adapted particularly for liquid phase operation; andFig. 2 a vertical section through an apparatus adapted to two-. phaseliquid-vapor operation.

The invention is primarily predicated upon our discovery that cyclicorganic compounds may be oxidized directly by molecular oxygen withoutthe intervention of active agents, by contacting them with oxygen in aclosed system at'an. elevated temperature and under a pressure substantially greater than the vapor pressure of the compound at thereaction temperature.

7 The invention is applicable to the oxidation of compounds of carbonhaving a closed ring structure, especially the aromatic and relatedcompounds, and an important feature is that the oxidation may becontrolled to prevent disrup: tion of the ring, or to retain in theoxidized prodnot at least one closed ring nucleus where the startingsubstance contains more than one ring. If benzene is treated inaccordance with the invention, the ring is broken, apparently becausethe splitting of an oxygen molecule in effecting oxidation of onehydrogen of the benzene ring leaves the other oxygen atom in such ahighly reactive state that it attacks another hydrogen atom, weakeningthe ring and causing its rupture. This untoward effect is apparentlyabsent or greatly repressed where one or more nuclear hydrogen atoms arereplaced by a side chain or other group which is more readily oxidizedthan the inert hydrogen atoms attached to the nucleus. Accordingly, theinvention particularly contemplates the oxidation of (a) substitutedbenzene, or aromatic, compounds, and especially the oxidation of purelyaliphatic side chains attached to the nucleus, examples of suchcompounds being toluene and the xylenes, (b) polynuclear or condensedring compounds, for example naphthalene, and (c) nahpthenes orhydroaromatic compounds, for example cyclohexane. All such compounds arefor brevity of reference herein comprehended by the term cyclic organiccompound.

Although the invention is especially applicable to the oxidation ofhydrocarbons of the type referred to, it may be applied to othersubstances, such as substances initially containing oxygen, for example,cresols, aldehydes, and/or other cyclic organic compounds.

As previously stated, prior commercial processes have invariablyemployed a catalyst, an alkali, or oxygen-liberating or other auxiliarymaterials. All such substances are herein cojointly referred to asactive agents, and under the invention as described none of them areessential.

In the practice of the invention the compound is treated with anoxygen-containing gas, and air will in most cases be whollysatisfactory. However, pure oxygen, ozone, and other oxygencontaininggases may be used.

In accordance with the invention, the total pressure in the system ismaintained at least at the vapor pressure of the reacting compound atthe temperature of thereaction, but preferably it is considerably inexcess of that value, and most suitably it is substantially in excess ofthe critical pressure of the compound. The reaction is carried out at anelevated temperature in excess of the melting point of the compoundbeing oxidized, and in the preferred practice it is above the normalboiling point of the compound but below that critical for the compound.

The temperature may be controlled in part by regulating theconcentrationof oxygen with respect to that of the material undergoing oxidation, forexample by admitting oxygen at such a rate with respect to theoxidizable substance that the heat evolved will not cause an excessivetemperature, or by dilution with an inert gas. However, in the course ofour researches we have found that the temperature of highlyexothermicgas-liquid reactions may be controlled readily to provide uniformity oftemperature throughout the reaction zone by vaporizing and condensing inthe system one or more components of its liquid phase, and that thismeans is especially applicable to direct oxidations of the typejustreferred to. In other words, the, temperature of a gasliquidreaction may be controlled directly by regulation of the total pressureon the system, as will be more fully explained hereinafter.

The invention may be practiced in various ways. For example, thematerial, liquefied if it is solid at normal temperatures, may betreated with an oxygen-containing gas, and when sufficient gas has beendissolved in the liquid material, the liquid-gas solution is passedunder pressure into a reactor which has been preheated to a suitabletemperature. The liquid is preferably saturated with oxygen to an amountsufiicient to effect the desired oxidation.

This proceduremay be practiced in connection with any suitableapparatus, for example that shown in Fig. 1.- This apparatus comprises asaturator 1 having an inlet conduit 2 provided with a branch 3 connectedto a source of oxygencontaining gas, such as an oxygen cylinder 4, and abranch 5 connected to a source of the compound to be oxidized, forexample a cylinder 6 containing toluene. The toluene or other materialmay be forced into the saturator by means of an inert gas, for examplenitrogen, supplied through a pipe 7.

The liquid-gas solution is passed under appropriate pressure through aconduit 8 into a pressure reactor 9 supported in a heating bath 10, andin order to increase the exposure conduit 8 preferably terminates in acoil 11, most suitably of capillary tubing, disposed in the reactor. Thesolution may be forced through the reactor by means of a liquid which isimmiscible with it, such as ethylene glycol in the case oftoluene, whichis forced into the saturat'or from a container 12 through a pipe 13, asby a pump, or by means of nitrogen or other inert gas under pressure, orby any other suitable means. The heating bath, which may be moltenlead-tin alloy, is maintained at a constant temperature in any suitablemanner, as by an electrical heater, not shown.

The material forced through the reactor coil expands after leaving thereactor, and the products pass to a condensing system 14, wherecondensible substances are collected. The residual gases are passed fromthe condensers through a conduit 15 to a meter 16, and may be collectedin a gasometer for further use. All of the lines are provided withsuitable valves, as will be understood.

In the operation of this form of apparatus the compound or material tobe oxidized is contacted with molecular oxygen at an elevatedtemperature and under high pressure, and the reaction probably takesplace during passage of the compound through the reactor coil. Nocatalyst or other active agent is necessary, and our tests have shownthat the reaction is apparently not affected by the material of whichthe coil is composed, several widely diiferent metals having been usedfor this purpose, which indicates that the reaction is one of directoxidation by the molecular oxygen present.

The end products may be worked up in any suitable manner, to separateand recover unreacted material and the oxidized product or products,such procedures being familiar chemical engineering unit processes. Theexit gases may contain carbon monoxide and/ or dioxide and otherproducts, depending upon the type of gas initially used and the materialbeing treated, and where air has been used, they are generallyimpoverished of oxygen and rich in nitrogen. Such tail gases may beworked up to recover desirable constituents, or they may be used asinert pressure media in the process, any unnecessary excess beingdiscarded.

The temperature, pressure, gas concentration, length of exposure toreaction conditions, etc. will vary according to the material beingtreated, the product desired, and the concentration of oxygen in the gasand it is not poss ole to prescribe exact conditions for all materials.However, skilled workers may readily determine the conditions for anyparticular material, and they are further exemplified by the followingdata selected from tests which we have made.

If these runs toluene was oxidized an apparatus si lar to that justdescribed, pure oxygen under pressure being passed into the saturatoruntil the toluene had taken up an amount corresponding to that shown inthe oxygen column of the following table. lhe toluene-oxygen solutionwas then forced into the reactor, the temperature in the reactor beingmaintained constant during the run. Calculations based on the timerequired for passage of the charge gave the period during which onemolecule of toluene remained in the reactor, this being given in thetime column.

It will be observed that in this series of tests the total usefulproducts are about the same at 279 C. as at 305 0., but that the carbondioxide formation is substantially less at the higher temp rature.Furthermore, at a given temperature, no advantage is gained by longexposure to reaction conditions, the reaction apparently being veryrapid, as shown above as well by other experiments which we have inwhich substantially the same yields were obtained with exposures ofabout seconds. In these tests there was little, if any, carboniorinationf Adequate temperature control in the use of the apparatusjust described is eiiected by conduction of heat through the wall of thereaction tube. That is, the ratio of heat dissipating surface of thecapillary coil to the mass of reacting liquid within it is high. Also,the concentration of oxygen with respect to the reacting li 6. is low,and this combination of factors renders temperature control relativelyeas in an apparatus.

The invention also be practiced in other ways and in other apparatusthan those just described. For example, the oxidizin gas be passed intoa large charge of the compound at reaction temperature in a two-phaseliquid-vapor system. In such operation, large amounts of material mayreact durin any given interval, causing liberation of large amounts ofheat, and accurate and uniform teuipenture control throughout the entirereaction zone is essential. In prior practice of this nat e such exactcontrol has not been accomplished, because of the difficulty ofattaining compl te uniformity of temperature throughout the reactionmass even with the most modern heat exchanging systems. Our inventionovercomes these difficulties and affords highly uniform temperaturecontrol throughout the reaction zone.

As previously stated, the rate of reaction, and consequently the amountof heatliberated in unit time, may be regulated, to some extent atleast, by varying the concentration of oxygen with respect to thecompound undergoing oxidation, and one means of accomplishing this is bydilution oi the oxygen-containing gas with an inert gas, for example byrecirculation of oxygen-impoverished efliuent gases.

A major feature of our invention, however, resides in our discovery thatalmost perfect temperature control of exothermic gas-liquid reactionsmay be effected by absorbing heat of reaction by evaporation of one ormore components of the liquid reaction charge and in heating theunreacted In this embodiment, a charge of the material to be oxidized isplaced in a closed reactor provided with refluxing means and with meansfor heating the charge, and a suitable oxygen-containing gas is passedinto the liquid charge. Due to the heat of reaction, the temperature ofthe material rises, and heat must beremoved in order to maintain thereaction temperature. ,In accordance with this embodiment, use is madeof latent heats of evaporation of the reaction materials and the heatcapacity of the gases concerned for that purpose.

At any given temperature the liquid exerts a definite vapor pressure,and vaporization takes place, the amount of heat thus absorbed beingdependent upon the amount of vaporization taking place. Becausevaporization takes place into the inert or unccnsumed fraction of theoxidizing the amount of vaporization is in part controlled by the ratioof vapor pressure to total pressure. This ratio is determined by thetemperature and total pressure due to the vapor pressure or the reactingmaterial and the pressures exerted by the vnconsuined fraction of theoxidizing oxides of carbon, and other products of reaction. Therefore,by operating at a suitable pressure the ratio of vapor to inert gas isregulated and the temperature of these liquid-gas resystem, (2) alloxygen reacting, (3) no gaseous or volatile products formed, (4)materials preheated to reaction temperature, and (5) equilibrium between liquid and vapor. If Q equals the heat evolved per mol of oxygenreacting, n the mber of reels of material vaporized in absorbing thisheat, and V the molal heat oi evaporation of the material at reactiontemperature, then Q:ni/, and

n=% Eq. I.

If L represents the vapor pressure or the material, P the total pressurein the system, and 1' the ratio. of inols of inert gas to mole ofoxygen, then i i-e5 by substitution in this equation of the value of nfrom Equation 1,

With air as the oxidizing gas, this equation becomes Eq. H.

Eq. in.

q. IV.

If the materials are pumped to the reactor cold, and assuming about percent of the heat to be used in preheating,

0.2X1O0000+(3.76X6000) r P 400 oaxlooooo 850 pouncs.

In case the gas contains only 10 per cent of oxygen, per cent of theheat being consumed in preheating, the pressure would be P=400 =490pounds.

P=400 =1840 pounds.

Where air is used, r is fixed, and the pressure is determined by theheat to be removed. Where heat losses from the system are high, thepressure must be high, or too much liquid will be evaporated and thesystem will operate at too lowa temperature. Where heat losses are low,the pressure will still be above the Vapor pressure of the reactingliquid. If the pressure is maintained at that required for desiredreaction temperature, the heat will be removed as rapidly as it isevolved, but if the pressure is too high, an insufficient amount ofvapor will be removed per unit volume of oxygen and the temperature willrise until equilibrium is effected by vaporization. On the other hand,if the pressure maintained in the system is too low, an excessive amountof liquid will be evaporated, and the temperature of the material willbe below that desired.

Except for the assumption that no volatile products are formed, thefactors on which the development of the foregoing equations is based arejustified, because they can be substantially realized. Gaseous productswill generally be formed, however, and in this case, assuming nc=mols ofvolatile products per mol of oxygen, S=mo1s of material supplied to thesystem, Tr=reaction temperature, To and Tl=entering temperature of gasand material respectively, Cpg and CpZ=average molal heat capacity ofgas and material, then and solving from which the operating pressure fora given set of conditions may be calculated.

This modified procedure may be performed in various ways, one of whichmay be understood in connection with Fig. 2. The reactor shown comprisesa lower reaction chamber 20 provided with an inlet connection 21 forintroducing a charge 22 of material to be oxidized, and an upper refluxportion 23 having means for condensing vapors arising from the reactionzone. The condenser consists of an ordinary tube basket 24 around thetubes of which cooling water may be circulated, as by means of inlet anddischarge conduits 25 and 26. Chamber 20 is provided with means forheating the charge, such as an electric heater 27, and oxygen-containinggas is passed into the charge through an inlet pipe 28, means such as aspreader dome 29 being preferably provided to distribute the gasthroughout the charge. The apparatus is also provided with apressure-controlling valve 30 of any suitable type, preferably one whichis adjustable to automatically relieve the pressure at a predeterminedvalue. A pressure gauge 31 is also provided.

In the use of this apparatus it will usually be desirable to discontinueheating after the reaction has started, because the reaction may beregulated so as to continue it by the heat of oxidation, although theequations given show that heat input would permit the pressure to bedecreased to the vapor pressure of the compound. However, for reasons ofeconomy, such heat input is undesirable, and the minimum pressure willgenerally be considerably above the vapor pressure at the reactiontemperature, the useful pressures in most cases lying between about 750and 2500 pounds per square inch.

' The process may be performed in batch or continuous fashion. In batchoperation the reaction products may be withdrawn from connection 21. Inthe case of continuous operation fresh compound may be continuouslyintroduced through inlet 21, and partially oxidized liquid withdrawnbenefits to be derived from the invention. In

these tests, an apparatus embodying the constructional features shown in2 was used, and air was used as the oxygen-containing gas. In one run,toluene was charged into the reactor and heated to 280 0., thistemperature being maintained in the manner described by maintaining thetotal pressure at 1000 pounds per square inch. The reaction liquid wascycled continuously, and air was passed into the liquid in the reactorat a rate such that the inlet oxygen corresponded to 9.1 mol per cent.Upon analysis of the reaction mixture, it was found that the benzoicacid and benzaldehyde concentrations were 3.3 and 1.0 per centrespectively, ccrre sponding to oxygen conversions of per cent and 3.5per cent respectively. The conversion under te pounds, such ascyclohexane invention also provides for such cases. event, a materialmay be added to th lion d to of; oxygen to carbon dioxide was 11.6 percent. In a similar run at 280 C., with inlet oxygen corresponding to23.7 mol per cent, and the other conditions being essentially the same,the benzoic acid and benzaldehyde concentrations were 19.0 and 1.1 percent respectively, corresponding to oxygen conversions of 24.2 and 1.6per cent respectively. Stillhigher concentrations or benzoic acid in theliquid have been ob tained by further increasing the r tio of inletoxygen. Our experiments along t". s line have shown that under theconditions Ci these tests the benzaldenyde concentration remains in theneighborhood of about 1 per centgirrespective of any increase in benzoicacid. concentration, and accordingly the ratio of acid to aldehydeformation may lee-controlled. Tests made at tempera tures as low as 2200., using an input of 769 'ters per hour, corresponding to 21.2 mol percent of oxygen, have given benzoic acid and ben zaldehyde concentrationsof 15.1 and 1.9 per respectively, corresponding to oxygen con -1esionsof 26.6 and 1.97 per cent respectively.

Experiments with other types of cyclic cornpounds "have demonstrated thewide applicability 'of .the processes according to the invention toorganic compounds of the ex ple,-naphth ene ay beozridized to producephthalic anliydi ue, and oxygenated compounds may he made from a varietyof other cyclic con Gur tests with commercial xylene have -cated thattoluic aldehydes, acids and ;'drides may be produced. in ourinvestigatio s .xith cc oo": other than toluene, the procedi. e was typestated. For

' similar to that described hereinaoove.

' pressu e that adequate control is not provided,

our

or thi. depict posses result may arise where the material is d byreaction and the products do not Q sufdciently high vapor pressures. OurIn this act as a heet exchanging component. Sucla material shouldpossess a vapor pressure at, and its critical temperature should beabove, the temperature of reacti n, and it should be inert conditionsor" reaction. Likewise, it should be inert, miscible with the materialto be oxidized. For most purposes water is an id al heat exchangingmedium for such use, beit possesses a critical temperature in exigh atelevated temperatures, and it has n.- heat. In most cases some water edin these reactions, but because tion is normally low, its effect willnor consequence, and water may to the necessary 3 unt. Materials of thetype referred to are adde solely for their heat-exchanging properties,they do not enter into the reaction, and consequently are not activeagents as that term is used herein. They may also be used as a means ofintimately contacting oxygen with the compound to be oxidized. Thus asolution of oxygen in carbon tetrachloride may be mixed with thecompound either in the saturator or the two-phase procedure. In bothcases it provides an intimate commingling of the reactants, and in thesaturator procedure an inert material is added which modifiestheintensity of the reaction by acting as a diluent, while in theprocedure last described, the same result is achieved by theheat-exchange ing effect.

So far as we are now aware, it is characteristic of our invention thatthe major portion of the oxidized products retain their aromaticcharacter', and. where both aldehydic and acidic prod.- ucts are formed,the acidic compounds usually predominate. The ring is not broken intheoxidation, or, as in the case of polynuclear' cons pounds, at least"one ring nucleus remains where the ori .al compound was composed ofseveral ihis is an important benefit of the invenbecause it contributesto the production .of attractive yields of useful cyclic-compounds whichhave hitherto been made by indirect or expensive processes, or byprocesses which possessed various disadvantages.

The process according to the invention is simple, direct, productive ofgood yields at low cost, and renders unnecessary the use of activeagents with their attendant cost, and diificulty of sep aration andrecovery. A particularly important benefit is consequent upon directoxidation combined with accurate temperature control. Not only does theinvention provide ready and ,accu-- rate temperature-control, but, whatis of at least equal importance, it insures in large masses .of reactingliquids an almost perfect uniformity of temperature with substantiallyno temperature gradient or tendency to overheating at any point.

Claims generic to the process of oxidizing cyclic organic compoundsdisclosed herein together with claims to the oxidation of substitutedbenzene compounds, are contained in a Ecopending application, Serial No.424,904, filedconcurrently herewith. Another copending application,Serial 0. 424,905, claims-the process ofoxidizing naphthenes, and theprocess of controlling the temperature of reacting liquids which isdisclosed herein, isbroadly disclosed and claimed in-still anotherconcurrently filed copending application, Serial No. 424,907. All of theforegoing applies..- tions Were filed on January 31, 1930.

According to the provisions of the patent statutes, we have explainedthe principle and mode of operation of our invention, and haveillustrated and described what we now consider to be its bestembodiment. However, we desire to have it understood that, within thescope of the appended claims, the invention may be practiced otherwisethan as specifically illustrated and described.

We claim:

1. A process of partially oxidizing a compound of the group consistingof naphthalene and related condensed aromatic ring compounds in whichtwo rigs share two adjacent carbon atoms, comprising contacting a liquidbody of said compound with a gas containing free oxygen in a closedsystem while heated to an elevated temperature below the criticaltemperature of the compound and under a pressure substantially greaterthan the vapor pressure of the compound at said temperature, and therebydirectly oxidizing said compound and forming a partial oxidation,product thereof.

2. A process of partially oxidizing a compound of the group consistingof naphthalene and related condensed aromatic ring compounds in wh'ehtwo rings share two adjacent carbon atoms, comprising contacting aliquid body of said compound with a gas containing free oxygen in aclosed system, the compound being heated to a temperature intermediateits normal boiling and critical temperatures, and said gas being under apressure substantially in excess of the vapor pressure of the compoundat said temperature, and thereby directing oxidizing said compound andforming a partial oxidation product thereof.

3. A process of partially oxidizing a compound of the group consistingof naphthalene and related condensed aromatic ring compounds in whichtWo rings share two adjacent carbon atoms, comprising contacting aliquid body of said compound with a gas containing free oxygen in aclosed system, the compound being heated to a temperature intermediatethe normal boiling and critical temperatures, and said gas being under apressure substantially in excess of the critical pressure of thecompound, and thereby directly oxidizing said compound and forming apartial oxidation product thereof. 1

4. A process of partially oxidizing a compound of the group consistingof naphthalene and related condensed aromatic ring compounds in whichtwo rings share two adjacent carbon atoms, comprising contacting aliquid body of said compound with a gas containing free oxygen in aclosed system, said compound being heated to a temperature intermediateits normal boiling and critical temperatures in a closed system andunder a total pressure in excess of the vapor pressure of the compoundat said temperature, and while maintaining the liquid body at saidtemperature and pressure supplying said gas at a rate to substantiallymaintain the oxygen concentration.

5. A process of partially oxidizing a compound of the group consistingof naphthalene and related condensed aromatic ring compounds'in whichtwo rings share two adjacent carbon atoms, comprising passing a gascontaining free oxygen into a heated liquid body of said compound in aclosed system, supplying said gas to replace the oxygen consumed,maintaining a total pressure in the system substantially in excess ofthe vapor pressure of the compound at reaction temperature to cause saidliquid to vaporize and maintain the entire body uniformly at saidtempera ture, said temperature lying between the normal boiling andcritical temperatures of the compound, and condensing and returning thevaporized liquid to the system.

6. A process of partially oxidizing a compound of the group consistingof naphthalene and related condensed aromatic ring compounds in whichtwo rings share two adjacent carbon atoms, comprising passing a gascontaining free oxygen into a heated liquid body of said compound in aclosed system, supplying said gas to replace the oxygen consumed,maintaining a total pressure in the system substantially in excess ofthe critical pressure of the compound at reaction temperature to causesaid liquid to vaporize and maintain the entire body uniformly at saidtemperature, said temperature lying between the normal boiling andcritical temperatures of the compound, and condensing and returning thevaporized liquid to the system.

7. A process of directly oxidizing naphthalene, comprising passing a gascontaining free oxygen into a liquid body of naphthalene heated to atemperature intermediate its normal boiling and critical temperatures ina closed system, supplying said gas to replace the oxygen consumed,maintaining a total pressure in the system in excess of the vaporpressure of naphthalene at said temperature, and by vaporization ofnaphthalene in the system absorbing heat of reaction to maintain theentire liquid body uniformly at said temperature, said temperature ofthe liquid being determined by regulation of the 'total pressure in thesystem, and condensing and returning the vaporized naphthalene.

8. A process of directly oxidizing naphthalene comprising contactingliquid naphthalene with molecular oxygen in a closed system at atemperature intermediate the normal boiling and critical temperatures ofnaphthalene and under a pressure substantially in excess of the vaporpressure of naphthalene at said temperature.

HENRY O. FORREST. PER K. FROLICH.

